Liquid pitch produced upon thermal cracking of heavy petroleum oil or coal tar in a reactor has heretofore been transported by pumping after the recovery from the reactor. In such a pumping transportation of the liquid pitch, however, coke which has deposited on the inside wall of the reactor often detaches therefrom and intrudes in a lumpy state into the pitch. This sometimes causes clogging in the suction port of a pump and/or piping to hinder the transportation of the liquid pitch, resulting in a serious effect on the continuous operation of the thermal cracking system. As stated above, continuous and stable transportation for the liquid pitch is difficult at present.